Coating equipment



April9,1940. R.BOICE 2,196,894-

- comma EQUIPMENT,

Filed April 21, 1938 f? 1/3553]! Boz'ce INVENTOR.

W C" W ATTORNEY; v

meant-em n'a-r coating machinesfl-the sheet to be coated is passed over suitable .itransverse,

Patented Apr. 9 1940 UNITED- STATES PATENT OFFICE COATING EQUIPMENT 7 Russell Boice, Newburgh, N. Y., assignor to E. I. du Pont de Ncmours & Company, Wilmington,

Del., a corporation of Delaware a lication April 21, 1938, Serial No. 203,256

' 3 Claims.

roll "d 'belo the-form of a continuousuhiform p'r'ewdusiy -rollers instead-ioflthedoctor knife'for the applithe oct'or roller-i move erit if-the s'he driven in f the direction of fbeing'"coated.' It has also oppo'sit'e direction of mOVEm'GXItZOfIthE sheet bedrive-the doctor'roller' at a-speed different from the rate of movement of the sheet passing under The conventional doctor knifeis satisfactory for spreading the base coats on a sheet but is notaltogether satisfactory for applying the final finishing coats since any insoluble particle or foreign matter which collects under the knife causes streaks or scratches in the finished product. Further, in the case of doctor knife coating any unevenness in the surface being coated causes an uneven amount of the finishing coat to be deposited and hence a variation in finish is obtained which is very objectionable. Still further, the doctor knifeis not suitable'for applying a final protective coat to a variegated surface such as printed or stenciled material. When the variegated surface passes under the doctor knife, there is a slight drag of the coatlng composition which has a solvent action on the base material, and the various colors are streaked or smeared as a result of the said dragging action.

Some of the disadvantages of the doctor knife for applying finishing coats to flexible sheets are overcome to a certain extent by the 'use of a driven 'doctor roller. The driven doctor rollers, however, are objectionable since they do not deposit a uniform film on a smooth surface. As is the case when a finish of contrasting color to the base material or when a dull finishing composition is applied to a bright finished base material, there results a mottled effect on the finished product which is extremely objectionable.

This invention has as an object the provision of an apparatus to apply finishing coats to a been p'i'oposed .touse doctor flexible sheet material which overcomes the disadvantages of the prior art apparatus.

A further object is the provision of an apparatus the use of which insures an exceptionally uniform application of a finish coat by means of oneor more undriven rotatable doctor rollers. A still further object is the provision of coat: 1 ing equipment which insures the absence 'of,a""" mottled appearance in the finished product. 1 Other objects will appear as the description of;

the invention proceeds.

These objects are accomplished by meansbf an improved coating head which comprises an undriven rotatable doctor roller to appl'y'or spread the coating composition in the'form of a film' and a smaller. auxiliaryundrlven rotatable doc ,tor roller located immediately behind the larger primary doctor roller to smooth or trowel the film spread by the first doctor roller, the two doctor rollers operating in conjunction with an endless belt which carries the sheet to be coated under the said doctor rollers. v

In the drawing the single figure is a sectional elevation of the coating head with the various parts arranged according'to the present invention as will be apparent as the description proceeds. In the single figure l0 and I2 represent two rotatable rolls around which an endless belt 9 is placed. This belt supports the fabric to be coated shown as 8. Located above the belt and fabric are two doctor rollers 2 and 3. The former is a primary undriven doctor roller and the latter is an auxiliary undriven doctor roller. The material used in coating the fabric, such as nitrocellulose jelly, is shown as I3. Another vertical adjusting roller indicated as H is located beneath the two doctor rollers over which the endless belt passes. This roll is adjustable vertically to increase the tension on'the endless belt 9. Ears (not shown) may be placed at the ends of the doctor rollers 2 and 3 to. prevent the coating composition from running over the edge.

In the operation of the apparatus according.

to the present invention, the flexible sheet material 8 is unwound from the unwind (not shown) I and passed over tension rollers (not shown) to the endless rubber'blanket 9, which carries the sheet material 8 under ,the doctor rolls 2 and 3 and into any suitable type of drying apparatus. The endless rubber blanket is mounted on two rollers l0 and II. The first roller Ill isadjustable horizontally to regulate the tension of the endless blanket, the second roller I2 is located at a suitable distance from the first roller, usually about 14 to 16 inches in the same horizontal plane as roller III. The roller I2 is driven by any suitable mechanism. Between rollers I0 and I2, and behind doctor rollers 2 and 3 there is located a vertical adjusting roller to further regulate the tension of the rubber blanket, as well as regulating the direction of travel of the sheet material after passing under roller 3. The doctor rollers 2 and 3 are mounted in bearings and are rotated by the material passing under the rollers. which is pressed against the' rollers by the endless rubber blanket 9.

The coating composition, such as a cellulose derivative composition dispersed in organic sol vents, is delivered on the sheet 8 immediately in front of the undriven rotatable doctor roller 2. The doctor roller 2 spreads an uneven film of the coating composition on the sheet material 8, which would have a Streaky. mottled appearance if it were not for the action of roller 3. The roller 3 has a wiping or smoothing action, similar to a troweling action, which tends to reduce the size of the streaks and prevent the mottled appearance. The streaky, mottled effect is very pronounced or accentuated when a cellulose derivative finishing coat having a color or lustre contrasting to the base material is applied to an unembossed or slightly embossed cellulose derivative coated fabric which has a relatively smooth surface.

It is very important that the second roller 3 be smaller than the first roller 2 since the size of the streaks in the deposited film after drying is in direct proportion roller 3. In the preferred embodiment of this invention the diameter of the primary doctor roller 2 is 1% inches and the diameter of the auxiliary wiper doctor roller 3 is 1 /4 inches and the horizontal distance between the axes of the two rollers 2 and 3 is two inches. Since the size of the first roller 2 controls the amount of coating composition applied to the material being coated it is not practical to use a doctor roller which is appreciably less than 1% inches in diameter. The horizontal distance between the peripheries of the two rollers is of an inch. When the roll of coating composition 13 in front of roller 3 reaches a certain size the composition contacts roller 2 and is carried back to the roll of coating composition l3 in front of roller 2. With respect to the auxiliary roller it may be less than the preferred dimension which is 1 /4 inches in diameter. The smaller the second roller, the smaller the streaks in the coating composition applled. However, the second roller should have a diameter which is greater than the height of the roll of coating composition which collects in front of the second roller. If

' the diameter of the second roller is less than the height of the roll of coating composition which collects in front of the second roller the coating composition will flow over the roller and damage the sheet materi being coated.

For practical purposes e size of the streaks or mottled appearance resulting from the use of an auxiliary roller 1% inches in diameter is not objectionable since the streaky mottled effect resulting from a roller this size is not visible to the casual observer. However, a wiper roller or smoothing roller which is appreciably greater than 1 /4 inches in diameter produces a Streaky mottled effect in the coating which is objectionable.

After passing under the two undriven doctor rollers 2 and 3 the material being coated enters a heating chamber where the solvents are to the size of the second volatilized and recovered. The heating chamber may be of any conventional type or that disclosed in U. S. Patent 2,107,275 which issued February 8, 1938, to W. T. Anderson and J. M.

Henry.

Where the streaky mottled effect is not objectionable the smoothing or wiping doctor roller may be eliminated entirely. It is also possible to obtain special decorative effects with the use of only one undriven doctor roller, in which case conventional masking tape cut out in the form of designs is pasted onto the undriven doctor roller. At the edges of the cut-outs adhered to the doctor roller there is collected an excess of the coating composition which deposits the excess onto the sheet material 8 as it passes under the doctor roller. In this manner the outline of the cut-out is transferred to the sheet material. In this case the coating composition used in the last two passes is of a contrasting color or lustre to the first coat. The design which is in relief on the undriven doctor roller will be outlined on the sheet material being decorated. The conventional masking tape used for finishing automobiles is desirable due to its low cost and the ease with which it may be readily attached and detached.

It is also possible to employ the double roller coating device above described with a conventional horizontal coating head without the aid of the rubber blanket. In this modification the two undriven rotatable doctor rollers are located between two transverse rollers in the same plane. The sheet material to be coated passes over the first transverse roller and under the two undriven rotatable doctor rollers and overthe second transverse roller. In this case two doctor rollers push down on the sheet material with sufficient pressure that the sheet material passing under the undriven doctor rollers will rotate the said doctor rollers. In this modification considerable tension isrequired on the sheet material being coated in order that it will be sufficiently taut to rotate the undriven doctor rollers.

The apparatus disclosed has been found to be completely effective in the prevention of the objectionable mottled surface appearance in pyroxylin coated fabrics. The present invention reduces production cost since it makes possible the application of the same amount of coating composition in a uniform film with one pass through the coating machine, which previously required two passes. Another advantage of the apparatus of this invention is that it provides a means for finishing variegated pyroxylin surfaces without smearing or streaking the separate colors.

A still further advantage of the present invention is that there is provided a means for applying a uniform surface film on an embossed surface. Prior art expedients, such as doctor knife application of a finishing coat to an embossed surface deposited the coating composition in the valleys of the grain and scraped the tops clean of the finishing composition.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof; and, therefore, it is not intended to be limited except as indicated in the appended claims.

I claim:

1. A coating machine for applying cellulose derivative compositions to a moving fabric which comprises two supports over which the said fabric passes and a plurality of undriven doctor rollers located between the said supports and in contact with the said moving fabric the first of the said rollers being the largest.

2. The apparatus of claim 1 in which there are two doctor rollers the first beingv approximately two inches in diameter and the second being approximately-one and one-quarter inches in diameter, the horizontal distance between the axes of said two doctor rollers being approximately two inches.

3. A machine for coating fabrics with cellulose derivative compositions which comprises two horizontal rollers, an endless belt passing over the said rollers, two doctor rollers, the first of which is' larger than the second, means for passing the fabric to be coated over the endless belt and under the said doctor rollers.

RUSSELL BOICE. 

